In the field of medical treatment and graphic arts, there have been concerns in processing of imaging materials with respect to effluent produced from wet-processing, and recently, reduction of the processing effluent is strongly demanded in terms of environmental protection and space saving. There has been desired a photothermographic dry imaging material for photographic use, capable of forming distinct black images exhibiting high sharpness, enabling efficient exposure by means of a laser imager or a laser image setter.
Known as such a technique are photothermographic image recoding materials comprising an organic silver salt, light-sensitive silver halide and a reducing agent on a support, as described in U.S. Pat. Nos. 3,152,904 and 3,487,075 by D, Morgan and B. Shely, and D. H. Klosterboer, “Dry Silver Photographic Material” (Handboook of Imaging Materials, Marcel Dekker Inc. page 48, 1991).
Such photothermographic image recording material which does not any solution type processing chemical, can provide users a simple and environment-friendly system.
In one aspect, this photothermographic image recording material contains light-sensitive silver halide as a photosensor and an organic silver salt as a silver ion source, which are thermally developed usually at 80 to 140° C. by a reducing agent included to form an image, without performing fixation. However, the photothermographic image recording material, in which an organic silver salt and light-sensitive silver halide are contained together with a reducing agent, easily causes fogging after raw stock and after subjected to thermal development, exposure to light over long period results in an increase of fogging.
As a technique for enhancing storage stability of photothermographic image recording material and improving fogging, there were disclosed techniques regarding improvement of organic silver salt, as described in, for example, JP-A No. 2000-62325, 2002-196446 and 2004-53985 (hereinafter, the term, JP-A refers to Japanese Patent Application Publication).